Bacteria are usually something you see a doctor to fight. But more and more, physicians are sending their patients to the store to stock up on live microbes.

That's the trend Jane Beran has noted over 30 years behind the counter at Jane's Health Food Market in Omaha, Neb. She's selling more products that contain probiotics -- good bacteria that have been shown to improve health.

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She said there are constantly new products coming to the market.

The Food and Agriculture Organization of the United Nations in 2001 defined probiotics as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.

Basically, these are bacteria that instead of causing infections actually make a person healthier.

Possible Health Benefits Emerge

There are about 100 trillion microbes that colonize a human body at any time, according to Mary Ellen Sanders, a microbiologist and leading expert on probiotics. Probiotics are often isolated from this reservoir of natural bacteria in the body.

But why should you add them to your diet?

Their primary use has been in prevention and treatment of diarrhea, especially when associated with use of antibiotics. Antibiotics not only kill the bacteria they were prescribed for, but they kill some good bacteria in the gut, which can cause trouble. Probiotics taken with antibiotics keep the good bacteria in action during the course of antibiotics.

"If you've been on an antibiotic, some people think that they do very well to take (probiotics)," Beran said. "A lot of people have a vicious cycle where you go off your antibiotic for two or three months, then get an infection again because your body's weak."

But research is starting to show all kinds of other advantages to regular use of probiotics, including fewer sick days, treatment of irritable bowel syndrome and even show promise for helping people who are lactose intolerant.

Allergy sufferers may find relief. Women who experience yeast infections may also benefit from taking probiotics.

In an 80-day Swedish study, workers taking probiotics took 10 sick days, compared with 23 sick days for workers not taking probiotics. And if you're stressed out, Shape magazine encouraged readers to take a probiotic to prevent cramping, bloating and gas that may result.

Consumer Reports said probiotics can prevent eczema, especially in children who were given the probiotic for the first six months of life. And children in at study done at a day care also benefited from probiotics. The group taking them had significantly fewer fevers, clinical visits, absences and prescriptions for antibiotics.

Where Do I Find Them?

New products are coming to market all the time claiming probiotic benefits. They include yogurts, cheese, chocolate bars, soy drinks, pudding, juices and a myriad of supplements.

Registered dietitian Carrie Miller, who is an extension educator for Douglas County, Neb., said the best way to get probiotics is through food.

"When it comes in a food source, your body knows how to use it," Miller said.

Miller said her family has added yogurt to their diets as they strive to put good bacteria to work for them.

Beran said she offers probiotic supplements, powders, liquids and chewables at prices ranging from $7.99 to $50. She said she's seen a trend in recent of years of more people asking for them. She credits more advertising, such as for Dannon's Activia yogurt and more recommendations by doctors. She said food makers are now even offering probiotics for pets.

In 2003, the total U.S. market for probiotics was valued at $143.9 million, NutraIngredients.com reported.

Sanders said she agrees that food is a good source of probiotics, but not all foods -- and not even all yogurts, which are widely believed to deliver probiotics with their advertised live cultures -- are created equal.

"The problem is that many of the yogurt products on the market haven't been formulated to contain adequate numbers of effective probiotics. Plus, I'm not sure, even as a specialist, if a particular yogurt is going to contain the right numbers. Choose yogurts made by companies invested in doing research on their products," Sanders said.

That includes products by Dannon, Stonyfield and Yoplait. Sanders has consulted for Dannon and Yoplait.

Sanders said consumers should probe a food or supplement company's Web site for documented research that shows studies on its products and their levels of delivered probiotic strains. There are plenty of products on the market that claim probiotics benefits, but research done in Seattle showed that "30 percent of the samples had contaminants, and 20 percent of the brands had no (bacterial) growth."

For people to experience a benefit from probiotics, they have to get the right strain and the right dose, and much of the science on that is still developing.

"There are lots of controlled human studies on the many different probiotic strains out there, but not too many individual products have a compelling number of studies on them. The research dwindles significantly," Sanders said. "As far as translating the science into specific medical recommendations, that is still emerging."

Still, consumers who do a little research on the products they purchase and who take the long view in terms of what probiotics may add to their health can see some benefits to adding a little bacteria to their diets.

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